It is well known that many polymeric materials may be dissolved in, or dispersed on essentially the molecular level so as to form a gel, with appropriate liquid vehicles provided that there is a high mutual compatibility between the polymeric material and the liquid vehicle. Dissolution or gel formation is typically accomplished by contacting the polymer and vehicle at ambient to relatively elevated temperatures. It is generally accepted in the art that an increase in temperature will speed dissolution of the polymer as will an increase in surface area as by comminution of the polymer into relatively small particles. Often, dissolution is accomplished by refluxing boiling vehicle or solvent over polymer particles.
Polyisobutylene, for example, is recognized to be soluble in hydrocarbon solvents such as kerosene and the like as is shown in U.S. Pat. No. 3,215,154 but its rate of dissolution is slow. Patentees teach heating the polymer-solvent mixture so as to increase the speed of dissolution and also recommend shredding or grinding the polymer to a particle size of 40 mesh or finer. Even with use of these techniques, a number of hours are required to fully dissolve the polymer in the solvent.
Because many polymeric materials are relatively soft and resilient, they are extremely difficult and often impossible to comminute by conventional grinding techniques. Even after comminution, the so-formed particles tend to stick and clump together thus negating the practical effect of such comminution.
It is also known to comminute relatively non-brittle materials, including rubbery polymers such as polyisobutylene, by cooling the materials below their embrittlement temperature using refrigerants. A cryogenic comminution system for such purposes is described in U.S. Pat. No. 3,771,729.
Polymeric materials dissolved or dispersed in liquid vehicles find use in a number of different applications. One such general application includes film forming as by casting, spraying, brushing or otherwise applying the polymer solution to a surface. The liquid vehicle is then removed, usually by evaporation, to leave a polymer film upon the surface. Cast films may be dense, in which case they are used as intrusion barriers or they may be somewhat porous and be used as breathing films or separation membranes. Sprayed or brushed films are most often applied as barrier films. Polymer solutions may also be used to form fibers by spinning, extrusion, or similar techniques. In film or fiber forming applications, it is generally advantageous to utilize a relatively concentrated solution of polymer in the liquid vehicle. Many commercial adhesives are also concentrated polymeric solutions.
There are a number of specialized uses for relatively dilute solutions of particular polymers in solvents. One such specialized use that has been the subject of extensive research is the reduction of friction in liquids flowing through conduits or around objects.
Hydrodynamics theory and practice demonstrate that the drag or friction caused by flowing liquid in a conduit increases the energy requirements to transport that liquid. This fact is particularly noticeable in the transportation or movement of hydrocarbons in pipelines as energy requirements increase as the square of the flow. It is recognized that increasing pumping power for flow augmentation can exceed conduit pressure limitations with accompanying deleterious effects. The pressure drop in a pipeline as liquids are pumped therethrough is a manifestation of this drag or friction.
Various means have been tried to reduce the undesirable effects of friction mentioned above. The addition of friction-reducing agents is described, for example, in U.S. Pat. Nos. 3,215,154; 3,682,187; 3,687,148; and 3,910,856. However, little success has been obtained by such additives because of the high cost or unavailability of the additive; the cost of effectively adding the additive to the hydrocarbons and dissolution therein, which may require many hours; the incompatibility of the additive with the subsequent use of the hydrocarbons; or the like. Thus, U.S. Pat. No. 3,215,154 describes, to reduce friction, intermixing with liquid hydrocarbons certain polyisobutylene resins as shredded, pulverized or ground solids, preferably of a particle size no greater than 40 U.S. standard screen scale. Natural rubber is also described as operable, but not as effective as polyisobutylene resin. The rate of solution of the polyisobutylene is described as slow; in what is described as an effective embodiment, polyisobutylene of 1020 U.S. standard screen scale particle size required stirring for two hours, with the necessity of an additional time required for complete solution. To decrease the time for dissolving the resin, as is described in the patent, the hydrocarbons can be heated up to about 200.degree. F. Also, the preparation of shredded, pulverized or ground polyisobutylene by usual means for subsequent dissolution causes degradation of the polymer; i.e., causes a reduction of molecular weight in some of the polymer molecules through shearing action and the heat generated thereby. Since it is known that friction reduction is dependent on long chain polymer molecules of relatively high molecular weight, such prior methods of shredding, pulverizing or grinding causes a reduction of the effectiveness of the polyisobutylene or other long chain polymers. Furthermore, the particles so prepared, when in contact with each other prior to introduction into the liquid hydrocarbons tend immediately to conglomerate into large masses, especially as fresh surfaces contact other fresh surfaces. The tough, strongly adhered polyisobutylene mass dissolves in hydrocarbon liquids only with difficulty and slowly, as above described. In fact, the stirring action over the long time required to dissolve a polyisobutylene mass causes additional shearing and degradation of the polymer molecules to the detriment of its friction-reducing properties.